Oil plug

If the plug is stripped it will never tighten, and that obviously is a problem. Solutions, depending on severity, may involve simply replacing the plug itself, or retapping hole, to inserting a helicoil, or replacing the oil pan. Don't reply on rubber grommets or teflon tape as a stopgap fix since a leak can spell disaster for the engine.

First of all make sure you are getting the correct plug. Then if the threads are bad in the oil pan an oversize plug that will cut its own threads can be used.